added proper top-level failure handling in evaluate

Signed-off-by: Konstantin Läufer <laufer@cs.luc.edu>

src/main/scala/behaviors.scala

@@ -1,17 +1,21 @@
 package edu.luc.cs.laufer.cs371.expressions
 
+import util.Try
+
 import Expr.*
 
 object behaviors:
 
-  def evaluate(e: Expr): Int = e match
+  private def evaluateR(e: Expr): Int = e match
     case Constant(c) => c
-    case UMinus(r)   => -evaluate(r)
-    case Plus(l, r)  => evaluate(l) + evaluate(r)
-    case Minus(l, r) => evaluate(l) - evaluate(r)
-    case Times(l, r) => evaluate(l) * evaluate(r)
-    case Div(l, r)   => evaluate(l) / evaluate(r)
-    case Mod(l, r)   => evaluate(l) % evaluate(r)
+    case UMinus(r)   => -evaluateR(r)
+    case Plus(l, r)  => evaluateR(l) + evaluateR(r)
+    case Minus(l, r) => evaluateR(l) - evaluateR(r)
+    case Times(l, r) => evaluateR(l) * evaluateR(r)
+    case Div(l, r)   => evaluateR(l) / evaluateR(r)
+    case Mod(l, r)   => evaluateR(l) % evaluateR(r)
+
+  def evaluate(e: Expr): Try[Int] = Try(evaluateR(e))
 
   def size(e: Expr): Int = e match
     case Constant(c) => 1

src/test/scala/Main.scala

@@ -1,27 +1,31 @@
 package edu.luc.cs.laufer.cs371.expressions
 
+import util.{ Success, Failure }
 import org.scalatest.funsuite.AnyFunSuite
 
 import behaviors.*
 import TestFixtures.*
 
 object Main:
   def main(args: Array[String]): Unit =
-    println("p = " + complex1)
-    println("evaluate(p) = " + evaluate(complex1))
-    println("size(p) = " + size(complex1))
-    println("height(p) = " + height(complex1))
-    println("q = " + complex2)
-    println("evaluate(q) = " + evaluate(complex2))
-    println("size(q) = " + size(complex2))
-    println("height(q) = " + height(complex2))
+    process("p", complex1)
+    process("q", complex2)
+    process("f", bad)
+
+  def process(n: String, e: Expr): Unit =
+    println(s"$n = $e")
+    println(s"evaluate($n) = ${evaluate(e)}")
+    println(s"size($n) = ${size(e)}")
+    println(s"height($n) = ${height(e)}")
+
 end Main
 
 class Test extends AnyFunSuite:
-  test("evaluate(p)") { assert(evaluate(complex1) == -1) }
+  test("evaluate(p)") { assert(evaluate(complex1).get == -1) }
   test("size(p)") { assert(size(complex1) == 9) }
   test("height(p)") { assert(height(complex1) == 4) }
-  test("evaluate(q)") { assert(evaluate(complex2) == 0) }
+  test("evaluate(q)") { assert(evaluate(complex2).get == 0) }
   test("size(q)") { assert(size(complex2) == 10) }
   test("height(q)") { assert(height(complex2) == 5) }
+  test("evaluate(bad)") { assert(evaluate(bad).isFailure) }
 end Test

src/test/scala/TestFixtures.scala

@@ -40,4 +40,6 @@ object TestFixtures:
       Constant(5)
     )
 
+  val bad = Div(Constant(3), Constant(0))
+
 end TestFixtures